Why is my code returning none when it's supposed to return the following? What's the corre-CodePudding

def append_combine(w, b):
 
  for i in range (len(w)):
    a.join (w) 
    a.append(w) 
  
x = []      
print(append_combine(x, 2))

I'm trying to work this one to return the example test case below. It's returning none. I can't even append the first integer to the list. Help me.

x = []
append_combine(x, 2) # [2]
append_combine(x, 3) # -> [2, 3]
append_combine(x, 3) # -> [2, 3, 3] -> [2, 6]
append_combine(x, 3) # -> [2, 6, 3]
append_combine(x, 3) # -> [2, 6, 3, 3] -> [2, 6, 6] -> [2, 12]
append_combine(x, 4) # -> [2, 12, 4]
append_combine(x, 3) # -> [2, 12, 4, 3]
append_combine(x, 5) # -> [2, 12, 4, 3, 5]
append_combine(x, 5) # -> [2, 12, 4, 3, 5, 5] -> [2, 12, 4, 3, 10]
# Final value of x is [2, 12, 4, 3, 10]

CodePudding user response：

You function had few errors. Correct code will be:

def append_combine(listname, element):
    if len(listname) == 0 or  listname[-1] != element: # This checks If the
                                                       # list is empty or last 
                                                       # element is not same
        listname.append(element)
    else:
        listname[-1] = 2*element # This is unnecessary with the loop so you can
                                 # remove it


    # This loop checks all duplicates
    while len(listname)>1 and listname[-1] == listname[-2]:
        listname.pop()
        listname[-1] = listname[-1] * 2
    return listname

x = []
x = append_combine(x, 2) # [2] Since the Function is returning a list, 
                         # you need to assign it to the list x
x = append_combine(x, 3) # -> [2, 3]
x = append_combine(x, 3) # -> [2, 3, 3] -> [2, 6]
x = append_combine(x, 3) # -> [2, 6, 3]
x = append_combine(x, 3) # -> [2, 6, 3, 3] -> [2, 6, 6] -> [2, 12]
x = append_combine(x, 4) # -> [2, 12, 4]
x = append_combine(x, 3) # -> [2, 12, 4, 3]
x = append_combine(x, 5) # -> [2, 12, 4, 3, 5]
x = append_combine(x, 5) # -> [2, 12, 4, 3, 5, 5] -> [2, 12, 4, 3, 10]
# Final value of x is [2, 12, 4, 3, 10] 
print(x)